1. Field of the Invention
The present invention relates to devices for the fire stopping of plastics pipes.
2. Description of the Prior Art
Plastics pipes which pass through fire-resisting walls or floors in a building represent a potential fire hazard. In the event of a fire, the plastics pipe is liable to melt thus creating a void through which hot gases may pass thereby spreading the fire to the space on the other side of the wall or floor. In order to avoid this effect, fire regulations may require that where a pipe passes through a fire-resisting wall or floor, means are provided for blocking a void which may be formed if the pipe should melt.
One previously proposed method of blocking a void which may be formed by a melting pipe involves the use of a mechanical shut-off device comprising a metal closure plate, usually actuated by gravity or a spring bias to displace the pipe as it softens and thereby cover the resulting hole in the wall or floor, the plate being attached to a bracket or other mounting assembly secured to the wall or floor adjacent the pipe. In addition to simply covering the hole, it is necessary that a shut-off device of this type should, after reaching the closed position, provide across the opening a seal of sufficient gas tightness that hot gases under pressure in the fire compartment should have a sufficiently low rate of passage through the now covered opening that temperature rise conditions outside the fire compartment do not exceed test standards, or alternatively, that no collapse due to heat softening of plastic pipework outside the fire compartment can occur.
The sealing tightness of such a device can be improved by application of a variety of chemical materials which intumesce on heating and expand to fill any cracks or gaps which may be left between the metal plate and the area around the hole. Selection of such intumescing materials must be made with care to ensure that they do not obstruct the movement of the plate and prevent a full mechanical closure from taking place. Relevant properties of such chemical intumescing materials are the temperature at which intumescence begins to occur and the stiffness or strength of the foam generated. In practice it is found that intumescent chemicals of the carbon char forming type are suitable, but unfortunately these materials have the characteristic of burning away at the higher temperatures encountered at later stages of the fire. The best of these materials would not exceed 30 minutes of effective sealing performance under fire conditions.
A further problem associated with the use of such purely mechanical shut-off devices is that for long duration fire performance--say in excess of 2 hours--the moving shut-off plate needs to be of heavily insulated construction so as to prevent transmission of unacceptable amounts of heat through the plate itself and thence through the opening which it covers. In practice, mechanical devices required for performance to a 2 or 3 Hour Rating require to be of bulky construction and are objectionable both from a cost and from a building installation point of view. For this reason there is a preference to use a device known as a fire stop collar which comprises an intumescent packing surrounding the pipe within the floor or wall, rather than on the surface of the floor or wall. Devices of this type are disclosed, for example in U.S. Pat. No. 4,221,092 and French Patent Specification No. 2,235,328.
However, with such fire stop collars, the rate at which they can operate to close a softened plastic pipe within a wall or floor is limited by the rate at which heat transmission can reach the packing through the face exposed to the fire. In floor installations, it is found that collars of appropriate design can function adequately for uPVC pipes in nominal diameter sizes from 32 mm up to 100 mm. Above 100 mm in size, the collar does not act to close the pipe quickly enough and needs to be supplemented by the use of a mechanical shut-off device of the type described above which acts to close off the pipe opening at the time when the pipe first softens.
A similar consideration applies to smaller sizes of pipe when connected to floor drains and wastes such as from showers, bathrooms, and urinals. In such configurations, when the pipe within the fire compartment burns through, hot gases are free to issue from the floor grating and can ignite any combustibles which may be present in those immediate areas. This condition is quite distinct from that in which the plastics pipe runs continuously through the opening in the wall or floor, because hot gases are contained within the pipe, the walls of which remain relatively cool for sufficient time into the fire period for the fire stop collar to become activated and close the opening. Test conditions for this floor waste configuration require that temperatures measured in the actual floor grating opening cannot exceed 180.degree. C. rise above ambient at any time from the onset of fire conditions. A fire stop collar used alone cannot satisfy this requirement and it is necessary to supplement it by a mechanical cut-off device with immediate action upon softening of the pipe.
Mechanical shut-off devices of the type so far described tend to be at least as expensive as the fire stop collars, and there is an appreciable extra cost in fixing such devices in their mounting position on a wall or the soffit of a building floor. Moreover, the bulk of such a device can be a significant hindrance to the operations of the plumbing contractor.
A requirement exists for a low cost mechanical shut-off device which can be used in conjunction with fire stop collars and like devices.